Contact combustion-type gas sensors for detecting quantities of constituent carbon monoxide, which is a non-combusted gas in, for example, and exhaust gas, having high sensitivity to only non-combusted gasses such as carbon monoxide, have been known conventionally. (See, for example, Japanese Unexamined Patent Application Publication H8-226909 (“JP '909”) (Pages 3-4 and FIG. 1)).
In the contact combustion type gas sensor set forth in JP '909, the gas detecting element and supplementary elements that structure a bridge circuit are supported on metal pins that are secured by penetrating through an insulating base, and these elements are covered by a cap. The gas sensing element includes a temperature measuring resistor and an oxidation combustion catalyst layer that is coated onto the temperature measuring resistor, where the oxidation combustion catalyst layer is made from a fine powder of an a ferric oxide carrying a gold catalyst, and an alumina powder carrying a platinum catalyst and a palladium catalyst.
Additionally, the temperature measuring resistor and the oxidation combustion catalyst layer that is coated thereon are exposed directly in the exhaust gas that includes the non-combusted gas, for example, to convert the increase in temperature of the oxidation combustion catalyst layer concomitant with the combustion of the non-combusted gas into a change in the resistance value of the temperature measuring resistor, so as to detect the quantity of the non-combusted gas constituent through a bridge circuit that includes supplementary elements.
In the contact combustion-type gas sensor such as set forth in JP '909 there are shortcomings such as the overall size being large, the sensor itself tending to increase costs, and there being constraints on the location of installation. Because of this, in recent years extremely small contact combustion-type gas sensors that use MEMS (Micro-Electromechanical Systems) technology have been used.
In a gas sensor such as set forth above, there are cases wherein gasses that are a hazardous environment to the sensor structural materials have been selected as being subject to measurement, and there has also been, for example, dust and the like, causing service life of the sensor to be reduced by this type of measurement environment. The shorter the service life of the sensor, the more frequent the maintenance (or the more frequently the sensor is replaced), producing a problem in terms of ensuring operation and in terms of operating costs.
The present invention considers the effect on the service life of the catalyst layer and the temperature measuring resistor being in direct contact, and provides a gas sensor chip, and a gas sensor provided therewith, that solves this problem to enable stabilized output characteristics over an extended period of time.